The most common reason for removal of a lens from the eye is the condition od lenticular opacity known as a cataract which occurs primarily in aged people. Previously these patient shad to wear a thick, aphakic over-refraction or a contact lens. This was to compensate for the loss of the human lens which is a major focusing element in the eye. Some people have great difficulty in tolerating the thick glasses. Many have difficulty adjusting to contact lenses and manipulating them. A majority of these patients are unable to tolerate extendedwear contact lenses becaue of dryness in their eyes and the threat of infection.
Today, 95% of the cataract operations performed in the United States involve implanting introocular lenses. Before the introduction of the expansile, hydrogel form of intraocular lenses, the initial insertion in the cornea was large, sometimes more than 7 mm to accommodate the lens and protruding loops. The lens was inserted through the large incision and positioned in the anterior or posterior chamber according to lens design and the needs of the patient. An incision of such size required more post-operative care and caused irritaion, discomfort to the patient, and higher degrees of astigmatism caused by corneal deformation secondary to sutiring. With the advent of expansile, hydrogel intraocular lenses of the type disclosed and claimed in U.S. Pat. No. 4,556,996, the size of the incision was drastically reduced and, therefore, required fewer stuures.
Technology introduced by Staar Surgical of Monrovia, Calif. has already significantly affected cataract surgery. Over 5,000 silicone intraocular lenses have been implanted to date under FDA investigative protocol in the United States. This technology is based on deformation methods as described in U.S. Pat. No. 4,573,998. It does not involve dehydration to maintain deformation.
There is newer technology which is based upon thermo-labile characteristics of hydrogels using low transition temperatures to deform and modify lens configurations for lens implantation. Essentially, these lenses are heated and compressed to smaller shapes and cooled to freeze the material below its transition temperature before it is implanted into the eye where it warms and returns to its original shape and size. This technology, which is distinctly different from the present invention, relies on transition temperatures which allows the compression of an elastic material at a high temperature and reduction of the temperature to "freeze" the material in its deformed state.
The present invention uses the hydrated elasticity to allow deformation under compression during deformation. The material is able to maintain the ideal deformed state due to the rigid nature of the dehydrated hydrogels. This unique concept avoids the need of the injectors or devices for the direct implantation of the materials in the silicone technology. It also avoids the extremely difficult technology of temperature constancy for the thermo-labile products.
Expansile intraocular lenses were designed to take advantage of the swelling and expansion upon hydration of hydrophilic materials. This permitted the lenses prior to implantation to be smaller than other implants or previously non-expansile artificial lenses since the expansile lenses are hydrated by the fluid present in the normal eye and expand to the predetermined desired optically correct size. The intraocular lenses are composed of a dry, solid hydrophilic material capable of expansion by absorbing the fluid pressent in the eye by hydration to a final diameter of from about 5 mm to about 14 mm to reach the predetermined optically correc tlens for the particular patient. These dehydrated lenses have a minimum diameter of about 2 mm and a maximum diameter of about 5 mm in the dry state which, of course, is less than the diameter of existing lenses. This permitted the implantation of intraocular lenses through an incision corresponding to less than 5 mm diameter compared to the non-expansile intraocular lenses which required an incision of at least 7 mm and up to 10 mm.
The need for still smaller intraocular lenses for use primarily in cataract surgery has been recognized recently. While gains in minimizing the trauma of cataract surgery to the elderly patients who are the primary victims of cataracts have been substantial as the result of using expansile hydrogel intraocular lenses and newer lens technology, some of these gains have been negated by the relatively large size of the lenses which still require relatively large incisions, insertion devices and tecyhnologically difficult maneuvering. All operations, of course, require an incision into the eye. The incision must, of course, be large enough to remove the old lens, preferably by phacoemulsification, and insert the new, yet kept as small as possible to minimize trauma to the patient.
It is an object of this invention to fabricate an intraocular lens that can be inserted through a very small phacoemulsification wound and yet provide all the optical qualities of larger lenses now in use.
It is another object to fabricate expansile, hydrogel intraocular lenses capable of returning to their original sizes after compressive deformation and dehydration which will allow insertion through small, phaceomulsification wounds.
Still another object of the invention is to provide an improved expansile, hydrogel intraocular lens which is deformed prior to the time of implantation by compressive forces so that it can pass in its deformed configuration through very tiny incisions.
Still another object of the invention is to reduce trauma and post-operative astigmatism and to decrease the physical and visual rehabilitation time following small incision cataract surgery.